Fibroblast growth factors (FGFs) are known to play an important role in embryogenesis, tissue homeostasis, and metabolism via FGF receptor (FGFR) signals (Non Patent Literature 1). In humans, there are 22 FGFs (FGF1 to FGF14 and FGF16 to FGF23) and 4 FGF receptors (FGFR1 to FGFR4; hereinafter, collectively referred to as “FGFRs”) having a tyrosine kinase domain. These FGFRs are each composed of an extracellular region comprising a ligand binding site composed of 2 or 3 immunoglobulin-like domains (IgD1 to IgD3), a single-pass transmembrane region, and an intracellular region comprising the tyrosine kinase domain. FGFR1, FGFR2, and FGFR3 each have two splicing variants called IIIb and IIIc. These isoforms differ in the sequence of approximately 50 amino acids in the latter half of IgD3 and exhibit distinctive tissue distribution and ligand specificity. It is generally known that the IIIb isoform is expressed in epithelial cells, while the IIIc isoform is expressed in mesenchymal cells. The binding of FGFs to FGFRs induces the activation of many signaling pathways (Non Patent Literature 1). As a result, FGFs and their corresponding receptors control a wide range of cell functions including growth, differentiation, migration, and survival.
The abnormal activation of FGFRs is known to participate in particular types of malignant tumor development in humans (Non Patent Literature 1 and 2). Particularly, FGFR2 signal abnormalities such as the overexpression of FGFR2 and its ligand, receptor mutations or gene amplification, and isoform switching, have been found to be associated with cancer (Non Patent Literature 2, 3, 4, 5, 6 and 7).
As mentioned above, the possibility of FGFR2 as an excellent therapeutic target for cancer has been suggested. In fact, monoclonal antibodies against FGFR2 have been obtained and are under clinical trial (Non Patent Literatures 8, 9, 10, and 11).
For these reasons, the provision of methods capable of detecting expression of FGFR2 and its splicing variants is useful in the testing or diagnosis of FGFR2-related diseases such as cancer or of FGFR2 expression.
Many monoclonal antibodies which recognize human FGFR2 are known. However, very few of these known antibodies are capable of being used for immunohistological staining. For instance, only one clone known as 1G3 (Non Patent Literature 12) recognises denatured FGFR2 when fixed in formalin, which means it is capable of immunohistological staining. Neither antibody cross-reactivity to the denatured form of other FGFR families when fixed in formalin, nor selective recognition of the denatured human FGFR2 splicing variants IIIb and IIIc when fixed in formalin, have been reported.
A monoclonal antibody which selectively recognizes a denatured splicing variant IIIb of human FGFR2 fixed in formalin has been reported (Patent Literature 1). However, no monoclonal antibody which selectively recognizes a denatured human FGFR2 IIIc has been identified.